It is a convenient practice to physically separate a digital computer from the keyboard and display unit by which the computer is monitored and controlled. Actually the K.D.U. consists of two units, a cathode ray-type display and a keyboard. The cathode ray display or, as it is usually called, a monitor, and keyboard may be in the form of a single housed unit or, as more commonly today with microcomputers, the monitor and keyboard are separate. The most popular microcomputer presently in use is the IBM-PC microcomputer, and there are many units made by other manufacturers which generally employ the same or a similar arrangement for interconnecting a keyboard and monitor to a computer.
As a matter of convenience, there are separate electrical jacks on these computers for mating plugs, one plug connecting to a monitor cable and the other to a keyboard cable. The opposite ends of these cables have plugs which directly plug into the microcomputer video and keyboard jacks. Normally these cables are on the order of four to six feet in length, enabling some, but limited, separation of a monitor-keyboard work station from a computer. This typically requires that the computer and work station be generally located together.
It is to be appreciated, however, that there are situations, in fact, many, where it is desirable to separate the computer and a workstation. This may be by virtue of space limitations or because of environmental considerations, the latter sometimes including an inhospitable environment for a computer. Additionally, situations occur wherein it may be desirable to locate a computer and a workstation having a color monitor in a control room situation and locate an inexpensive monochrome monitor, also connected to the computer, in a factory or manufacturing environment, or other inhospitable environment, a distance away from the computer. In this case, and using software for a color computer which uses color backgrounds for highlighting, and a different color of data on the highlighted backgrounds, problems arise when the signal for a color monitor is split and one of the color signals fed to the monochrome monitor. Particularly, in some PC-type computers having a Video Graphics Adapter (VGA) video output card which provides color or monochrome video signals in accordance with the type of monitor connected to it, and in the instance where a monochrome monitor is coupled thereto, the VGA driver card will translate the color data into monochrome signals and output these signals on the green video signal line to the monochrome monitor. This conversion of color signals to monochrome signals is accomplished, in accordance with IBM tm VGA standards, by selecting the highest intensity of the color signals as the intensity at which to output all the data to the monochrome monitor. For example, if any of the color data is of high intensity, the VGA card outputs all the data at high intensity to the monitor. Likewise, if none of the color data is of high intensity and some is at normal intensity, all the data will be output at normal intensity and the same for the low intensity signals. The problem here is that if color data and a color background of like intensity is displayed, such as a normal intensity green background having normal intensity red data thereon, the conversion process results in normal intensity white background with normal intensity white data thereon at the monochrome monitor, resulting in the data being indistinguishable from the background.
This particular problem has been in existence for at least four years, with solutions to overcome the problem being software oriented. These solutions utilize various symbols to denote colors in a color environment and do not represent color data in a manner that is pleasing to the eye or readily discernable as a contrast, such as the aforementioned colored background and differently colored letters.
In addition to the aforementioned problem relating to data being indistinguishable from a background, the problems relating to signal interaction between keyboard and video signals when these signals are applied to non-shielded conductors of an extended-in-length cable are attended to as disclosed herein and in patent application Ser. No. 07/488,710, filed Mar. 5, 1990.
It is, therefore, the object of this invention to provide simple, reliable circuitry that receives color data signals from a computer and converts the signals to monochrome signals for an analog monochrome monitor wherein color conversion to a monochrome signal results in a gray scale such that every color and shade thereof is represented by a discrete, unique shade of gray and to further provide circuitry that will accept color signals from a computer, split these signals, and provide color signals to a color monitor and provide monochrome signals wherein colors are represented by a gray scale to a monochrome monitor.